Comcast would invest $1 billion and Time Warner would put as much as $500 million into the venture. Sprint and Clearwire have been trying to raise $3 billion to build a WiMax network.

The company would be operated by Sprint Nextel and Clearwire, said the source, who spoke on condition of anonymity to the Washington Post because talks are ongoing.

In exchange for funding the WiMax joint venture, the cable companies would get equity in the business and would be able to purchase wholesale access to the network to offer their own high-speed wireless data and voice services to customers, the people familiar with the discussions said.